Electrical insulator



g- 6, 1946- w. w. HIGGINS 2,405,425

ELECTRICAL INSULATOR Filed April 30, 19 2 Waldo Wiggins INVE 0R.

. Y/Zwl ATTORNEY.

Patented Aug. 6, 1946 ELECTRICAL INS ULATOR Waldo W. Higgins, Whitefish Bay, Wis, assignor to A. O. Smith Corporation, Milwaukee, Wis, a

corporation of New York Application April 30, 1942, Serial No. 441,199

9 Claims.

This invention relates to electrical insulators and has been applied in the construction of high tension insulating bushings and the like.

The principal object is to provide a ceramic enamel insulation of high dielectric properties.

Another object is to provide a bonding of the parts of an insulating bushing together by means of a ceramic enamel insulation.

An embodiment of the invention is illustrated in the drawing in which:

Figure 1 is a side elevation of a typical insulating bushing with parts broken away and sectioned to show the construction;

Fig. 2 is a perspective View of a plate prior to enameling;

Fig. 3 is an axial section through the plate after a substantial thickness of enamel has been fused thereon, the coating being shown in exaggerated thickness;

Fig. 4 is a similar section showing the application of the final coating of enameling material prior to fusing, the coating with the enameling material being exaggerated in thickness; and

Fig. 5 is a similar section showing the completed plate with its enamel coating ready for final assembly, the coating being exaggerated in thickness.

In carrying out the invention, the surfaces of the insulator parts to be joined are first coated with a vitreous or ceramic enamel having good bonding properties and a fine bubble structure and then additional coats of a substantially bubble-free enamel are applied and fired until an insulating coating of the proper thickness and free from flaws is obtained. The parts are th'en assembled and fused together in accordance with the general process of interfusing enamel coatings set forth in applicants copending application, Serial No. 441,201, entitled Joinder of porcelain enameled products, filed on even date herewith.

The first coat of enamel should be of fine bubble structure to secure a good bond with no large bubble formations and with freedom from fishscaling and other defects. The subsequent coatings should be of substantially bubble-free structure so as to prevent the propagation of bubbles through it.

If desired, the final coating of enamel prior to interfusion may be of a softer enamel, fusing at a lower temperature than the harder coats previously applied. This reduces the possibility of surface flaws which may destroy the dielectric properties of the enamel after interfusion. 7

Referring to the drawing, the electrical insulater shown in Fig. 1 comprises a conductor bushing l with a threaded axial shank 2, a plurality of spacer plates or rings 3, and a core plate 4 with an integral tubular shank 5, all of said parts being concentric and the bushing I, spacer plates 3 and core plate 4 being joined together by fused ceramic enamel 6 disposed therebetween.

The spacer plates 3 are of rolled steel plate of substantial thickness (ordinarily about A; of an inch) and have a, central opening 1 with the edges of the metal curved on a large radius to receive the enamel. The outer edges of the plates 3 are thinned to provide a gradual taper as at 8 from the maximum thickness for enameling and to provide a substantial air gap 9 between the edges of adjacent plates.

The inner surfaces of the conducting bushing l and of the core plate 4 are shaped similar to the spacer plates 3 for joining thereto.

The spacer plates 3 and corresponding surfaces of the bushing I and plate 4 are first coated with a ceramic enameling material of high fusion point and containing a clay that will produce a fine bubble structure to effect a permanent bond with the steel and to obtain freedom from fish-scaling and other defects. Suitable clays are the German Valender, Kentucky, Tennessee, and English Ball clays, or similar clays, which give a very fine bubble structure when fired under regular practice.

Following this first coat, a number of additional coats of ceramic enameling material, preferably of bubble-free characteristics, are applied and fired until a minimum total enamel thickness of from fifteen to twenty thousandths of an inch is obtained. The enamel should be of the hard type and fired for about ten minutes at about 1600 F.

As illustrated in Figs. 3 and 4, the coating of enamel tends to thicken when flowing in the firing operation at the flat portion of the surfaces immediately adjacent the curved or tapered edge portions. This tends to leave a thinner central portion on the flat surface of the plate which might effect entrapment of air when interfusing the parts.

In order to prevent this, a final coating of enameling material it is applied and brushed as illustrated in Fig. 4 and then fired to produce a coating which is crowned on the flat surface of the plate as illustrated in Fig, 5. The drawing illustrates the thicknesses of the coating as exaggerated to give an understanding of the process, In actual practice the difference in thickness may be very slight, but nevertheless, sufficient to make it advisable to apply the final coating referred to.

the coating beneath since the latter does not reach its fusion temperature on the last firing.

When the faces of the bushing l, the spacers 3 and the core plate 4 have been suitably enameled to the desired thickness, generally about fifteen to twenty thousandths of an inch, and inspection shows that there are no defects, the parts are assembled in the order shown in Fig. l, with the spacers 3 on top of the core plate t and the bushing l resting on the upper most spacer. many spacers 3 may be employed as desired. The members are all in axial alignment with the crowned or flat enameled faces of each spacer registering with the corresponding face adjacent thereto and in contact therewith.

After assembly as above described, a weight is applied on the bushing to press the members to gether with a predetermined force and the entire assembly is placed in a furnace and heated to a temperature from 100 to 200 firing temperature of the enamel. This heating is sufficient to soften the enamel without completely re-fusing the same and results in a bonding of the several enamel coatings together with out danger of producing the surface of the steel.

Where the last firing of enamel was carried out at about 1600 F. the heating for bonding the members together may be carried out at about 1.450 R, and where the F, it is possible to bond the parts together at about 1250 F. The heat should be sufiicient to soften the enamel, but not to substantially melt or gasify constituents of the enamel. The time of heating should be longer may be about minutes, depending somewhat upon the pressure applied and the temperature employed.

The weight to be applied to the members should be sufficient to apply a pressure on the contacting surfaces of enamel equal to at least one-half to three-quarters of a pound per square inch of final fused surface. Where a large number of spac ers are employed and it is desired to eliminate the weight of the spacers as a factor in applying pressure to the contacting enamel coatings, the assembly may be turned horizontal and supported in a suitable cradle with means to apply a prede termined pressure on the ends to provide a uniform and equal pressure on all of the surfaces. The pressure applied may vary somewhat with the thickness of the coatings.

The crowning of the enamel surfaces serves to provide a small area of contact therebetween at the start of the heating step, and as the enamel gradually softens the area of contact becomes progressively larger until complete contact is made and the two coatings merge and become interfused. This insures that no air or other contamination remains or is entrapped between the coatings.

The insulator fabricated as above described has the parts bonded together by the dielectric ceramic enamel and has been found to be superior to former insulators in many respects. The bond lower than the last defects from re-fusing at f final coat is fired at l350 than the firing time and L is mechanically strong, being capable of withstanding a pull of 3,000 lbs. per square inch in tension axially as against former porcelain insulators which could withstand a pull of only about 2,000 lbs. per square inch in tension. The electrical insulating strength is also very good, being as high as 500 volts per mil (.001) of enamel thickness at temperatures up to 300 F. The outer edge of the plates may be left free of enamel to provide for fiashover in case of overload.

Various embodiments of the invention may be employed within the scope of the accompanying claims.

The invention is claimed as follows:

, 1. The method of fabricating an insulator bushing having spacer rings with opposed surfaces, comprising coating the opposed surfaces of the rings with a ceramic enamel having its surface crowned at the medial line thereof, assembling said members with the crowned surfaces of the enamel coatings in pressure contact, and heating the members to a temperature below that employed for firing the enamel to soften the same and progressively increase the area of contact therebetween until said coatings are bonded together.

2. The method of fabricating a high tension insulator or the like, comprising coating the metallic members with a ceramic enameling material containing a clay that produces a, fine bubble structure upon firing, firing the coating material to provide a ground coat bonded to the metal, applying as many subsequent coats of a substantially bubble-free ceramic enamel as may be required to provide a final coating of said members of substantial thickness and free from flaws that would destroy the dielectric characteristics required of the coatings, assembling said members with said coatings in contact, and heating said members to a temperature substantially lower than the firing temperature of the enamel to soften the coatings while applying pressure thereto to effect a bonding of the contacting coatings together.

3. In the fabrication of a dielectric member, the coating of a plurality of metallic elements with a ceramic enamel free from ilaws which reduce the dielectric properties of the enamel, by first applying and firing a ceramic coating material containing a clay producing a, fine bubble structure and having good bonding characteristics, thereafter applying and firing thereon a coating of substantially bubble-free ceramic enameling material, assembling said elements with the coatings of adjacent elements in contact, and heating said elements to a, temperature substantially lower than the firing temperature of the enamel and sufficiently high to soften the coatings while applying pressure thereto to effect a bonding of the contacting coatings together.

4. In the fabrication of an electrical insulator, the coating of a plurality of metal members with a ceramic enamel free from flaws which reduce the insulating properties of the enamel, by first applying to the member a ceramic enameling material containing a clay giving a fine bubble structure, firing the same, thereafter applying and firing successive coatings of a substantially bubble-free ceramic enameling material to provide a predetermined minimum thickness of coating, assembling said members with the coatings of adjacent members in contact, and heating said membersto a temperature substantially lower than th firing temperature of the enamel and sufliciently high to soften the coatings while applying pressure thereto to effect a bonding f the contacting coatings together.

5. In the fabrication of an electrical insulator, the coating of a plurality of metal members with a ceramic enamel free from flaws which reduce the insulating properties of the enamel, by first applying to the member a ceramic enameling material containing a clay giving a fine bubble structure, firing the same, thereafter applying and firing successive coatings of a substantially bubble-free ceramic enameling material to provide a predetermined minimum thickness of coating, the last coating being applied in restricted areas to provide a substantially crowned thickness for the enamel, assembling said members with the coatings of adjacent members in contact, and heating said members to a temperature substantially lower than the firing temperature of the enamel and sufiiciently high to soften the coatings while applying pressure thereto to effect a bonding of the contacting coatings together.

6. In the fabrication of an electrical insulator, the coating of a plurality of metal members with a ceramic enamel free from fiaws which reduce the insulating properties of the enamel, by first applying to the member a ceramic enameling material containing a clay giving a fine bubble structure, firing the same, thereafter applying and firing successive coatings of a substantially bubble-free ceramic enameling material to provide a predetermined minimum thickness of coating, the last coating being brushed away from the outer areas prior to firing to provide an enamel surface that is crowned over a predetermined portion of the surface of the member, assembling said members with the coatings of adjacent members in contact, and heating said members to a temperature substantially lower than the firing temperatur of the enamel and sufliciently high to soften the coatings while applying pressure thereto to effect a bonding of the contacting coatings together.

7. In the fabrication of an electrical insulator, the coating of a plurality of metal members with a ceramic enamel free fro-m flaws which reduce the insulating properties of the enamel, by first applying to the member a ceramic enameling material containing a clay giving a fine bubble structure, firing the same, thereafter applying and firing successive coatings of a substantially bubble-free ceramic enameling material to provide a predetermined minimum thickness of coating, the last coating being of a softer enamel of lower firing temperature than the first to provide for a smoother outer surface for the enamel with less tendency to gasify in firing, assembling said members with the coatings of adjacent members in contact, and heating said members to a temperature substantially lower than the firing temperature of the enamel and sufiiciently high to soften the coatings while applying pressure thereto to effect a bonding of the contacting coatings together.

8. An electric insulator bushing comprising a plurality of metal members secured together by a substantially bubble-free high dielectric ceramic enamel material fused and bonded to the adjacent faces of said members and providing a substantial resistance against electrical breakdown.

9. In an electric insulator of the class described a spacer ring comprising a disk of metal of substantial thickness having a central opening with round corners at its edge and having the outer edge thinner than the body of the disk with a gradual taper in thickness merging with the body, and a ceramic enamel coating bonded thereto on the faces of said body portion and taper and on said rounded inner edge,

WALDO W. HIGGINS. 

